In the production of concrete articles, concrete aggregates and mixing water are mixed together to form concrete from which is manufactured concrete articles. After manufacture, the concrete articles must be cured and as well known in the art, the term "curing" refers to the time during which hydration or hardening of the cement takes place through chemical reaction between the cement and water during which the newly formed (green) concrete articles acquire their strength. Many types of curing techniques have been developed and at present, in the concrete block industry, the most widespread technique is low pressure steam curing. In the low pressure steam system, the green concrete articles are loaded into a kiln after which a sufficient quantity of steam is injected directly into the kiln to heat the internal kiln atmosphere to the designed temperature while, at the same time, maintaining a high degree of saturation thereby providing the combination of heat and moisture which accelerates the hydration and hardening of the cement.
One drawback of the low pressure steam system is that considerable energy is required to generate the steam which, in most low pressure steam systems, is maintained at a temperature on the order of 160.degree.-200.degree. F. It has been found that considerable heat energy is consumed in heating up the kiln surfaces (walls, roofs, floors, etc.), in heating up the steel pallets on which the block is stacked, and in heating up the steel racks which, if used, support the pallets in the kiln. In addition, heat energy is lost to the outside air due to conduction through the kiln walls and roof. Also, heat energy is required to heat up the volume of air within the kiln itself. In view of the continually escalating cost of fuel, careful consideration is being given to ways in which to conserve energy in not only the curing phase but in the entire process of concrete block production.